The invention relates to fluidized bed processes for reduction of iron ore and, more specifically, to a method for reforming the reducing gas used in the process.
U.S. Pat. No. 5,192,486 to Whipp is drawn to a plant and process for fluidized bed reduction of ore. This patent is representative of a process wherein iron oxide is passed through a series of ore reactors and contacted with reducing gas so as to provide a reduced or metallized iron product. Reducing gas for such processes is typically produced in special plants known as reformers. Typical reforming units are of the stoichiometric type, and use natural gas/carbon monoxide mixtures, steam reforming and partial combustion. Units for carrying out the first two types of reforming, specifically natural gas/carbon monoxide reforming and steam reforming, are very costly and use expensive catalysts.
The partial combustion method also has certain drawbacks, for example, the sulfur content of heavy hydrocarbons typically used as fuel tend to contaminate the metal products, and carbon deposition on relevant equipment is also a problem. Furthermore, in these processes, nitrogen builds up in the reactors and reducing gas, adversely affecting reducing quality of the gas.
In fluidized bed processes such as that disclosed in Whipp '486 ore is passed sequentially downwardly through a series of reactors while gas is passed serially upstream through the same reactors. It has been found that gas passing through the reactors entrains dust and particulate matter from the ore material being reduced, which dust or particulate matter can cause severe plugging and other complications in the reactor.
In light of the foregoing, it is clear that the need remains for a process wherein reducing gas is provided and the fluidized bed reduction process is carried out at reduced cost, with increased efficiency and with less tendency for plugging.
It is therefore the primary object of the present invention to provide a method for producing reducing gas for use in the fluidized bed process without expensive reforming equipment.
It is a further object of the present invention to provide a method for producing reducing gas in a manner which utilizes heat already present in the fluidized bed process so as to increase efficiency of the overall process.
It is another object of the present invention to provide a method for producing reducing gas in connection with a fluidized bed process which takes advantage of particulate or dust material entrained in partially spent gas, and which further inhibits the tendency toward excessive accretion or plugging in reactor equipment.
Still other objects and advantages of the present invention will appear hereinbelow.